1. Field of the Invention
This invention is related to a precision cleaning method and, more particularly, a cleaning method utilizing pressurized gases, such as carbon dioxide, along with solvents which are environmentally acceptable.
2. Description of the Prior Art
It is desirable to remove in a precise and repeatable manner organic, particulate, and ionic contamination from components and assemblies without the use of environmentally sensitive solvents (solvents considered to endanger the environment), water rinses, and extensive post-cleaning drying. It has been proposed to utilize carbon dioxide, alone and in combination with other solvents, to conduct cleaning. For example, U.S. Pat. No. 5,013,366 discloses a cleaning process using phase shifting (shifting to and from the supercritical phase) and dense phase gases wherein carbon dioxide is the preferred dense phase gas. This patent discloses that carbon dioxide may be mixed with co-solvents, such as anhydrous ammonia gas, and compressed to the supercritical state. This patent also discloses the general concept of utilizing carbon dioxide, co-solvents, and ultrasonic energy to enhance cleaning. U.S. Pat. No. 5,068,040 discloses that supercritical ozone dissolved in liquid or supercritical carbon dioxide or water is an excellent solvent/oxidant for inorganic material. However, the presence of water presents problems with water recycling and disposal. Finally, U.S. Pat. No. 2,617,719 discloses a method and apparatus for cleaning porous media, such as oil-bearing sandstone. The cleaning cell is supplied with a solvent and a dissolved gas, such as carbon dioxide. Used solvent is vented to the atmosphere. Solvent venting creates hazards to the environment which are unacceptable by today's standards.
Additional cleaning, extracting and stripping methods are shown in U.S. Pat. Nos. 4,879,004; 5,011,542; 4,788,043 and 5,143,103.
As intimated in the patents referred to above, supercritical carbon dioxide alone cannot remove all contaminants from parts and assemblies. The range of contaminants encountered includes low molecular weight organic compounds which are nonpolar in nature, high molecular weight nonpolar organic compounds, ionic compounds (such as fingerprints) and high molecular weight polar organic compounds (such as fats). It has been found that carbon dioxide cannot remove all of these contaminants, even when augmented with sonic or mechanical agitation.
Thus, it is an object of the present invention to provide a method and apparatus for precision removal of organic, particulate and ionic contamination from components and assemblies without the use of environmentally sensitive solvents, water rinses, and extensive post-cleaning drying.
It is a further object to capture the removed contaminants and automatically remove the contaminants from the cleaning system for disposal. It is a further object to allow for use of environmentally acceptable co-solvents while limiting the contamination of a workpiece by the co-solvent. It is a further object to avoid release of co-solvents to the atmosphere. It is a further object to provide separation and concentration of carbon dioxide, co-solvent and contaminants for ease of handling, storage and disposal.